This invention relates to methods and apparatus for use in the manufacture of foundry molds and cores wherein a gas phase catalyst is used to cure the resin binder of a sand-resin mixture from which the mold or core is to be made. More particularly, this invention relates to methods and apparatus for use in systems wherein the catalyst is in the liquid phase at standard conditions of temperature and pressure (25.degree. Celsius and 760 mm Hg.).
A popular group or family of catalysts for use in curing phenolic type resins is the tertiary amines such as dimethylethylamine and triethylamine. (See U.S. Pat. No. 3,409,579.) Since this resin-catalyst system is highly reactive, i.e., curing occurs almost instantaneously, it is common foundry practice to dilute the catalyst to concentrations (by weight) of below 25% in an inert carrier gas such as carbon dioxide or nitrogen and then blow the mixture into the mold or core box containing the resin coated sand.
The past method of introducing the above-noted catalysts, which are liquids at standard conditions of temperature and pressure, into the carrier gas stream is to either bubble the carrier gas through the liquid catalyst or to inject the liquid catalyst directly into the carrier gas stream via an injector or spray nozzle. These methods, however, do not provide any control over the catalyst concentration in the gas mixture and also are apt to introduce the catalyst into the mold or core as a fog or mist rather than a gas. Introduction as a gas is preferable because:
1. Speed of reaction is enhanced because of greater mobility of catalyst molecules in the gas phase over that of liquid phase molecules.
2. Residual catalyst in the cured core or mold results in fuming during metal pouring and defective castings. Common practice involves purging the core or mold with air prior to removing it from the forming box. Liquid phase catalyst requires greater amounts of air and longer cycle times which detract from over-all process economics.